Light emitting device

ABSTRACT

The disclosed light emitting device comprises at least one first light emitting element including at least one light emitting chip for emitting light having a wavelength of 400 to 500 nm and a phosphor; and at least one second light emitting element disposed adjacent to the first light emitting element to emit light having a wavelength of 560 to 880 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/514,761, filed on May 13, 2009, and claims the benefit of theNational Stage of International Application No. PCT/KR2007/006343, filedDec. 7, 2007, which claims priority from and the benefit of KoreanPatent Application No. 10-2006-0133498, filed on Dec. 26, 2006, andKorean Patent Application No. 10-2006-0138489, filed on Dec. 29, 2006,which are all hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device having lightemitting elements or light emitting cells for emitting light of ared-based wavelength, which is suitable for improving a Color RenderingIndex (CRI) property.

2. Discussion of the Background

Recently, light emitting elements driven under high voltage and AC powerhave been developed to be used for general illumination. Such a lightemitting element has been disclosed in PCT Patent Publication No. WO2004/023568(A1), entitled “Light-emitting device having light emittingelements” by Sakai et al.

A conventional light emitting element has a plurality of light emittingdiodes (hereinafter, referred to as light emitting cells) on a singlesubstrate, and the plurality of light emitting cells are connected inseries and reverse parallel through metal wires, which can be used bydirectly connecting to high voltage or an AC power source.

However, in order to use the conventional light emitting element forillumination, the light emitting element emits blue-based light and theblue-based light is applied to a wavelength converting substancecontaining a phosphor to be color converted, or the light emittingelement is implemented by mixing lights respectively emitted from red,blue and green light emitting elements.

However, since light emitted from the conventional light emittingelement has a low CRI, the natural color of an object cannot be clearlyshown when the light is thrown on the object.

FIG. 1 is a graph showing the CRI property when a blue light emittingchip is provided and a wavelength converting substance containing ayellow phosphor is applied to the blue light emitting chip.

Meanwhile, FIG. 2 is a graph showing the CRI property when lightsemitted from red, blue and green light emitting elements are mixed.

According to the conventional light emitting element, an intensity ofred-based light is extremely weak compared with those of blue- andgreen-based lights. In this case, it is difficult to express a red-basedcolor, and thus the CRI property essential to a light source forillumination may be lowered.

In particular, the CRI property (color rendering) is considered as beingvery important in the illumination facility market. Thus, it is requiredto improve the CRI property in order to use a light emitting diode (LED)as a light source for illumination.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light emitting devicesuitable for improving the CRI property to use an LED as a light sourcefor illumination.

According to an aspect of the present invention, there is provided alight emitting device, comprising: at least one first light emittingelement including at least one light emitting chip for emitting lighthaving a wavelength of 400 to 500 nm and a phosphor; and at least onesecond light emitting element disposed adjacent to the first lightemitting element to emit light having a wavelength of 560 to 880 nm.

Preferably, the first light emitting element is formed as a packagetype.

Preferably, the first and second light emitting elements are mounted ina molding member containing a phosphor.

Preferably, the first light emitting element is mounted in a firstmolding member containing a phosphor, and the second light emittingelement is mounted in a second molding member formed to cover the firstmolding member.

Preferably, the first light emitting element comprises a plurality oflight emitting cells, the plurality of light emitting cells areconnected in series to form at least a first array and at least a secondarray, and the first and second arrays are connected in reverse parallelto each other.

Preferably, the phosphor includes a yellow phosphor.

According to another aspect of the present invention, there is provideda light emitting device, comprising: a substrate; a plurality of lightemitting cells formed on the substrate, each of the light emitting cellshaving a lower semiconductor layer, an upper semiconductor layer formedon a portion of the lower semiconductor layer and an active layerinterposed between the lower and upper semiconductor layers; and wiresfor electrically connecting the light emitting cells, each of the wiresconnecting the lower semiconductor layer of one of the light emittingcells to the upper semiconductor layer of another adjacent one of thelight emitting cells, wherein at least one of the plurality of lightemitting cells emit light having a wavelength of 560 to 880 nm.

Preferably, the plurality of light emitting cells are connected inseries to form at least a first array and at least a second array, andthe first and second arrays are connected in reverse parallel to eachother.

Preferably, the light emitting cells except the light emitting cell foremitting light having a wavelength of 560 to 880 nm emit light having awavelength of 400 to 500 nm.

Preferably, a wavelength conversion substance for converting awavelength of light emitted from the light emitting device isadditionally disposed to an outside of the light emitting device, andthe wavelength conversion substance includes a yellow phosphor.

In the specification of the present invention, the term “Light emittingdevice” may be a chip or package type device. Thus, a chip-type lightemitting element having a plurality of light emitting cells formedtherein may be expressed as a light emitting device in some claims or aportion of the detailed description. Further, the term “Light emittingdevice” may be expressed as a device having at least one light emittingelement or at least one LED package. Furthermore, the term “Lightemitting element” may be used as an LED chip or an LED package havingthe LED chip.

According to the present invention, a CRI property necessarily requiredto use an LED as a light source for illumination can be considerablyimproved using a light emitting element or a light emitting cell foremitting light having a wavelength of 560 to 880 nm.

According to an embodiment of the present invention, in addition to atleast one first light emitting element having at least one lightemitting chip for emitting light having a wavelength of 400 to 500 nmand a phosphor, at least one second light emitting element for emittinglight having a wavelength of 560 to 880 nm is disposed in various forms,thereby relatively increasing intensity of light having a wavelength of560 to 880 nm. Accordingly, it is easier to express a color of awavelength of 560 to 880 nm, and therefore, the CRI property isimproved, whereby the LED is suitable for being used as a light sourcefor illumination.

According to another embodiment of the present invention, a lightemitting device is provided to have a structure in which at least one ofa plurality of light emitting cells formed on a substrate emits lighthaving a wavelength of 560 to 880 nm that is different from thewavelength (particularly, 400 to 500 nm) of other light emitting cells,and therefore, the CRI property is improved at a chip level, whereby alight emitting device suitably used as a light source for illustrationcan be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a CRI property when a yellow phosphor isapplied to a light emitting element that emits blue-based light.

FIG. 2 is a graph showing a CRI property when lights emitted from red,blue and green light emitting elements are mixed.

FIG. 3 is a circuit diagram schematically showing a configuration of alight emitting device according to an embodiment of the presentinvention.

FIG. 4 and FIG. 5 are a plan view and a sectional view illustrating afirst light emitting element in FIG. 3, respectively.

FIG. 6 is a graph showing a CRI property of a light emitting deviceaccording to the present invention.

FIG. 7 is a circuit diagram schematically showing a configuration of alight emitting device according to another embodiment of the presentinvention.

FIG. 8 is a view illustrating a package-type light emitting deviceaccording to a further embodiment of the present invention.

FIG. 9 is a view illustrating a package-type light emitting deviceaccording to a still further embodiment of the present invention.

FIG. 10 is a sectional view showing a light emitting element accordingto an embodiment of the present invention.

FIG. 11 is a plan view showing the light emitting element according tothe embodiment of the present invention.

FIG. 12 is a sectional view showing a light emitting element accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Thefollowing embodiments are provided only for illustrative purposes sothat those skilled in the art can fully understand the spirit of thepresent invention. Therefore, the present invention is not limited tothe following embodiments but may be implemented in other forms. In thedrawings, the widths, lengths, thicknesses and the like of elements maybe exaggerated for convenience of illustration. Like reference numeralsindicate like elements throughout the specification and drawings.

FIG. 3 is a circuit diagram schematically showing a configuration of alight emitting device according to an embodiment of the presentinvention.

Referring to FIG. 3, the light emitting device according to theembodiment of the present invention comprises a current stabilizingcircuit 1, a first light emitting element 2 provided with blue lightemitting chips and a yellow phosphor to thereby emit white light, and asecond light emitting element 3 provided with red light emitting chipsto emit light of a red-based wavelength, which are connected in series.

The first and second light emitting elements 2 and 3 are alternatingcurrent (AC) light emitting elements operated by AC power. A pluralityof light emitting cells are connected in series or parallel throughwires in each of the first and second light emitting elements 2 and 3and emit light when AC power is supplied.

Each of the light emitting cells provided in the first light emittingelement 2 has the blue light emitting chip and the yellow phosphor.Thus, the yellow phosphor converts a color of a portion of the bluelight (400 to 500 nm) and emits the converted light with another portionof the blue light, which is unconverted, from the blue light emittingchip provided in each of the light emitting cells, and thus white lightis emitted.

At this time, light emitted from the first light emitting element 2 hasa wavelength property as shown in FIG. 1.

Meanwhile, each of the light emitting cells provided in the second lightemitting element 3 comprises light emitting cells for emitting light ofa red-based wavelength (560 to 880 nm). The number of light emittingcells provided in the second light emitting element 3 may be determineddepending on a degree of emission of red light. The second lightemitting element 3 relatively increases intensity of red-based light.Accordingly, it is easier to express a red-base color, thereby improvinga CRI property.

FIGS. 4 and 5 are a plan view and a sectional view, respectively,illustrating the light emitting cells provided in the first lightemitting element 2 in FIG. 3. It will be apparent that the lightemitting cells provided in the second light emitting element 3 may befabricated in the same form as the light emitting cells provided in thefirst light emitting element 2.

Referring to FIGS. 4 and 5, the first light emitting element 2 comprisesa plurality of light emitting cells 100 on a substrate 10. Each of thelight emitting cells 100 comprises a lower semiconductor layer 20, anactive layer 30 formed on a portion of the lower semiconductor layer 20,and an upper semiconductor layer 40 formed on the active layer 30.Meanwhile, a buffer layer (not shown) may be interposed between thesubstrate 10 and the light emitting cells 100. For example, GaN or AlNmay be mainly used as the buffer layer. The lower and uppersemiconductor layers 20 and 40 may be n-type and p-type semiconductorlayers, or p-type and n-type semiconductor layers, respectively. Theactive layer 30 may be formed in a single or multiple quantum wellstructure. A first electrode (not shown) may be formed on a portion ofthe lower semiconductor layer 20, on which the active layer is notformed, and a second electrode (not shown) may be formed on the uppersemiconductor layer 40.

The light emitting cells 100 are connected so that the lowersemiconductor layer 20 of one of the light emitting cells 100 isconnected to the upper semiconductor layer 40 of another adjacent one ofthe light emitting cells 100 through a wire 50. At this time, if atleast a first array and at least a second array respectively connectedin series are formed and then they are connected in reverse parallelwith each other, it is possible to suppress generation of flickers eventhough the light emitting element 2 is connected to an AC power source.The wire 50 may be formed by a process such as a typical step cover orair bridge, but is not limited thereto.

FIG. 6 is a graph showing a relative spectrum power distribution foreach wavelength of the light emitting device according to the embodimentof the present invention.

Referring to FIG. 6, the light emitting device has the second lightemitting element 3 for emitting light of a red-based wavelength (560 to880 nm), thereby relatively increasing intensity of red-based light.Accordingly, it is easier to express a red-based color, therebyimproving the CRI property.

FIG. 7 is a circuit diagram schematically showing a configuration of alight emitting device according to another embodiment of the presentinvention.

Referring to FIG. 7, the light emitting device according to thisembodiment of the present invention comprises a first light emittingelement 4 having blue light emitting chips and a yellow phosphor to emitwhite light, and a second light emitting element 5 having red lightemitting chips to emit light of a red-based wavelength. The first andsecond light emitting elements 4 and 5 respectively have stabilizingcircuits 6 and 7 and are connected in parallel.

FIG. 8 is a view illustrating a light emitting device according to afurther embodiment of the present invention.

Referring to FIG. 8, a light emitting device 300 according to theembodiment of the present invention comprises two first light emittingelements 320 and 330 and a second light emitting element 340 disposedbetween the two first light emitting elements 320 and 330 on a singlesubstrate 310. Each of the first light emitting elements has a bluelight emitting chip for emitting light of a blue-based wavelength (400to 500 nm) and a yellow phosphor, thereby emitting white light, and thesecond light emitting element 340 has a red light emitting chip foremitting light of a red-based wavelength (560 to 880 nm).

Here, the first light emitting elements 320 and 330 may be lightemitting elements that are packaged to be individually used for highpower, and the second light emitting element 340 may be a light emittingchip that is not packaged but may be used on a small scale.

Thus, as the second light emitting element 340 for emitting red light isdisposed between the two first light emitting elements 320 and 330, ared-based wavelength is effectively compensated, thereby improving theCRI property.

FIG. 9 is a view illustrating a light emitting device according to astill further embodiment of the present invention.

Referring to FIG. 9, a light emitting device 400 according to theembodiment of the present invention comprises a first molding member 430containing a yellow phosphor.

In the first molding member 430, a first light emitting element 410having a blue light emitting chip for emitting light of a blue-basedwavelength (400 to 500 nm) and a second light emitting element 420having a red light emitting chip for emitting light of a red-basedwavelength (560 to 880 nm) are disposed on one slug (not shown). Asecond molding member 440 surrounds and protects the first moldingmember 430.

As the first and second light emitting elements 410 and 420 are disposedin one molding member, it is possible to reduce a mounting area thereof.In addition, a red-based wavelength can be effectively compensated,thereby improving the CRI property.

The present invention is not limited to the aforementioned embodimentsand various modifications and changes can be made thereto by thoseskilled in the art. The modifications and changes are covered by thespirit and scope of the invention defined by the appended claims.

For example, the first and second light emitting elements 410 and 420are disposed together in the molding member 430 containing the phosphorin the embodiment of the present invention shown in FIG. 9. However, asa modification, the first light emitting element 410 may be mounted inthe first molding member 430 containing the phosphor, and the secondlight emitting element 420 may be mounted in the second molding member440 covering the first molding member 430.

Hereinafter, light emitting devices according to further embodiments ofthe present invention will be described, which are configured so thatone of a plurality of light emitting cells formed on a substrate emitslight of a red-based wavelength (560 to 880 nm).

FIGS. 10 and 11 are a sectional view and a plan view of a light emittingelement having a light emitting cell for emitting light of a red-basedwavelength, respectively.

Referring to FIGS. 10 and 11, a plurality of light emitting cells 100are formed on a substrate 10. Each of the light emitting cells 100comprises a lower semiconductor layer 20, an active layer 30 formed on aportion of the lower semiconductor layer 20, and an upper semiconductorlayer 40 formed on the active layer 30. Meanwhile, a buffer layer (notshown) may be interposed between the substrate 10 and the light emittingcells 100. For example, GaN or AlN may be mainly used as the bufferlayer. The lower and upper semiconductor layers 20 and 40 may be n-typeand p-type semiconductor layers, or p-type and n-type semiconductorlayers, respectively. The active layer 30 may be formed in a single ormultiple quantum well structure. A first electrode (not shown) may beformed on a portion of the lower semiconductor layer 20, on which theactive layer 30 is not formed, and a second electrode (not shown) may beformed on the upper semiconductor layer 40.

The light emitting cells are connected so that the lower semiconductorlayer 20 of one of the light emitting cells 100 is connected to theupper semiconductor layer 40 of another adjacent one of the lightemitting cells 100 through a wire 50. At this time, if at least a firstarray and at least a second array respectively connected in series areformed and then they are connected in reverse parallel with each other,it is possible to suppress generation of flickers even though the lightemitting element 4 is connected to an AC power source. The wire 50 maybe formed by a process such as a typical step cover or air bridge, butis not limited thereto.

As described above, FIG. 1 is a graph showing a CRI property when awavelength converting substance containing a yellow phosphor is appliedto a blue light emitting element for emitting light of a blue-basedwavelength (400 to 500 nm). Referring back to FIG. 1, intensity ofred-based light is extremely weak as compared with blue- and green-basedlights. In this case, it is difficult to express a red-based color, andthus, the CRI property essential to a light source for illumination maybe lowered.

If at least one of the plurality of light emitting cells 100 is formedas a light emitting cell 200 for emitting light of a red-basedwavelength (560 to 880 nm) as shown in FIGS. 10 and 11, the CRI propertywith which the intensity of red-based light is relatively increased isobtained as shown in FIG. 6. Accordingly, it is easier to express ared-based color, thereby improving the CRI property.

As described above, the method of forming at least one of the pluralityof light emitting cells 100 as the light emitting cell 200 for emittinglight of a red-based wavelength is not limited particularly. Forexample, it is possible to use a method of removing at least one of theplurality of light emitting cells 100 through a laser lift-off (LLO)process and then bonding a light emitting cell 200 for emitting light ofa red-based wavelength to the place where the light emitting cell 100 isremoved.

Although a light emitting cell 200 for emitting light of a red-basedwavelength is positioned at the edge of the array in the embodiment ofthe present invention, this is provided only for illustrative purposes,and the light emitting cell 200 may be positioned inside of the array.

FIG. 12 is a sectional view showing a light emitting element accordingto a further embodiment of the present invention.

Referring to FIG. 12, a plurality of light emitting cells 100 are formedon a substrate 10. Each of the light emitting cells 100 comprises alower semiconductor layer 20, an active layer 30 formed on a portion ofthe lower semiconductor layer 20, and an upper semiconductor layer 40formed on the active layer 30. Meanwhile, a buffer layer (not shown) maybe interposed between the substrate 10 and the light emitting cells 100.The lower and upper semiconductor layers 20 and 40 may be n-type andp-type semiconductor layers, or p-type and n-type semiconductor layers,respectively. The active layer 30 may be formed in a single or multiplequantum well structure.

The plurality of light emitting cells 100 formed on the substrate 10 areflip bonded onto a submount substrate 11 through first and second bumps21 and 41. At this time, at least one of the plurality of light emittingcells 100 formed on the substrate 10 may be replaced with a lightemitting cell 200 for emitting light of a red-based wavelength (560 to880 nm).

A light emitting element having a plurality of flip-chip type lightemitting cells 100 and 200 with superior color rendering can befabricated by the method described above.

What is claimed is:
 1. A light emitting device, comprising: a firstlight emitting element comprising a light emitting chip and a phosphorand configured to emit light having a first wavelength; and a secondlight emitting element disposed adjacent to the first light emittingelement, the second light emitting element configured to emit lighthaving a second wavelength, wherein the phosphor is disposed on an upperportion of the light emitting chip, and the phosphor comprises a yellowphosphor, and wherein the second light emitting element is connected inseries or parallel with the first light emitting element.
 2. The lightemitting device of claim 1, wherein the first light emitting elementcomprises a plurality of light emitting cells connected in series witheach other.
 3. The light emitting device of claim 1, wherein the firstlight emitting element further comprises a first molding member to coverthe first light emitting element, and the phosphor is disposed in thefirst molding member.
 4. The light emitting device of claim 3, whereinthe second light emitting element is disposed outside of the firstmolding member.
 5. The light emitting device of claim 4, furthercomprising a second molding member covering the first molding member andthe second light emitting element.
 6. The light emitting device of claim1, further comprising a current stabilizing circuit, and the currentstabilizing circuit being connected in series with the first lightemitting element.
 7. The light emitting device of claim 1, wherein thesecond light emitting element is disposed between two first lightemitting elements.
 8. The light emitting device of claim 1, wherein thelight emitting chip comprises a plurality of light emitting cells, eachlight emitting cell being disposed on a substrate and comprising a lowersemiconductor layer, an active layer, and an upper semiconductor layer,and the light emitting cells are connected in series with each otherthrough wires.
 9. The light emitting device of claim 1, wherein thelight emitting chip comprises a plurality of light emitting cells, eachlight emitting cell being disposed on a submount and comprising a lowersemiconductor layer, an active layer, and an upper semiconductor layer.10. The light emitting device of claim 5, wherein the second moldingmember does not contain any phosphor.
 11. The light emitting device ofclaim 10, wherein the second molding member is domed shape.
 12. Thelight emitting device claim 1, wherein the first wavelength is in arange from 400 nm to 500 nm.
 13. The light emitting device claim 1,wherein the second wavelength is in a range from 560 nm to 880 nm. 14.The light emitting device claim 3, further comprising a third lightemitting element, wherein the third light emitting element is configuredto emit light having the second wavelength, and wherein the firstmolding member covers the third light emitting element.
 15. The lightemitting device claim 14, wherein the second wavelength is in a rangefrom 560 nm to 880 nm.
 16. The light emitting device claim 8, wherein atleast one of the plurality of light emitting cells emits light having awavelength in a range from 560 nm to 880 nm.
 17. The light emittingdevice claim 9, wherein at least one of the plurality of light emittingcells emits light having a wavelength in a range from 560 nm to 880 nm.